The present invention generally relates to electrical circuitry and more particularly, to a circuit for cutting or removing a direct current component or DC component (referred to as a DC cutting circuit hereinafter) suitable for use in an output circuit, for example, a microwave oscillator or the like.
Commonly, in an output circuit such as a microwave oscillator, etc., it is necessary to take out, i.e., pass through as the output of the circuit, only the oscillation output. For this purpose, referring to FIGS. 1(A) and 1(B), it has been a conventional practice to employ a DC cutting circuit in which a gap G is formed in the course of a micro-strip line L for effecting signal transmission from an input side circuit such as an oscillator or the like (not shown) to an output side circuit such as a mixer circuit, etc. (not shown), with a layer-built chip capacitor C being disposed thereat connecting the two sides of the gap G as shown in FIGS. 1(A) and 1(B). In FIGS. 1(A) and 1(B), a grounding electrode Eg is formed generally over the entire reverse surface of a substrate B made, for example, of alumina or the like, with the chip capacitor C being connected to the micro-strip line L by solder S as illustrated.
However, in the known DC cutting circuit as described above, there are such disadvantages that cost tends to be increased by the employment of the layer-built chip capacitor C, and that, since the capacitor C itself is not provided with a filter characteristic, it is possible for a signal not required such as a spurious signal, etc., to be undesirably transmitted. In addition, when the working frequency becomes high, for example, up to the order of 10 GHz, the influence due to parasitic inductance of the chip capacitor is increased, and it becomes doubtful whether or not its function as a capacitor is correctly performed, thus presenting a problem with respect to the effectiveness of the capacitor.
In some of the prior art DC cutting circuits, an attentuator of the .pi. type or the T type is inserted in series with the layer-built chip capacitor as referred to above in order to improve frequency stabiity against variation of load. However, an arrangement including such an attenuator requires extra procedures such as attaching a chip resistor or trimming a thick or thin film resistor for the formation of the attenuator, thus resulting in an increase in labor costs.